1. Field of the Invention
The present invention relates to a linear motor, and more particularly, to a linear motor in which a gap portion is defined by magnetic poles or teeth having characteristic shapes.
2. Description of the Related Art
In a linear motor, magnetic poles on a stator (or moving element) and teeth on a moving element (or stator) face one another to form a gap. The cogging torque of the linear motor is settled depending on the shapes of the magnetic poles and the teeth that are opposed to the poles. In order to lower the cogging torque, therefore, various magnetic poles or teeth having special shapes have been proposed.
FIG. 11 shows a prior art example of a stator or moving element (slider) of which the magnetic poles are formed of permanent magnets. The stator or slider is constructed in a manner such that a plurality of permanent magnets 1 are arranged parallel to one another on a plate 10 that is formed of a magnetic material such as iron. If each permanent magnet 1 is cut in a direction parallel to the direction of relative movement of the slider with respect to the stator, in the example shown in FIG. 11, the gap-side external shape of its cross section is a straight line 31. Thus, the gap-side surface (the surface opposite the plate 10) of each magnet 1 is flat.
FIGS. 12 to 14 show alternative prior art examples of the stator or moving element of which the magnetic poles are formed of permanent magnets. If each of permanent magnets 1 that are arranged side by side on a plate 10 is cut in a direction parallel to the direction of relative movement of the slider with respect to the stator, in the example shown in FIG. 12, the gap-side external shape of its cross section is a circular arc 32. Likewise, in the example shown in FIG. 13, the gap-side external shape of the cross section of each permanent magnet 1 is a parabola 33. In the example shown in FIG. 14, the gap-side external shape of the cross section of each permanent magnet 1 is a hyperbola 34.
As described above with reference to FIGS. 11 to 14, many attempts have been made to vary the shapes of the magnetic poles to lower the cogging torque.